linux-kernel - Re: [PATCH] kernel:async function call:introduce async_run

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Date:	Wed, 13 May 2009 19:11:44 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	tom.leiming@...il.com
Cc:	arjan@...radead.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Ming Lei <tom.leiming@...il.com>
Subject: Re: [PATCH] kernel:async function call:introduce
 async_run_inatomic(v2)

On Wed, 13 May 2009 23:51:39 +0800,
tom.leiming@...il.com wrote:

> From: Ming Lei <tom.leiming@...il.com>
> 
> The purpose of this function is to offer a simple way to schedule an
> asynchronous thread from an atomic context, because there are not any
> functions which can create and start a kernel thread in atomic contexts
> now. We use async_running_no_sync as running list to make callers that
> don't want to synchronize on cookies, so can avoid some side effects for
> async_synchronize_full().
> 
> Part of note for async_run_inatomic and some guideline is from Cornelia Huck.
> 
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> Signed-off-by: Cornelia Huck <cornelia.huck@...ibm.com>
> ---
>  include/linux/async.h |    2 ++
>  kernel/async.c        |   23 +++++++++++++++++++++++
>  2 files changed, 25 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/async.h b/include/linux/async.h
> index 18ce92b..9ff62af 100644
> --- a/include/linux/async.h
> +++ b/include/linux/async.h
> @@ -16,6 +16,8 @@
>  typedef u64 async_cookie_t;
>  typedef void (async_func_ptr) (void *data, async_cookie_t cookie);
> 
> +extern int async_run_inatomic(async_func_ptr *ptr, void *data);
> +
>  extern async_cookie_t async_schedule(async_func_ptr *ptr, void *data);
>  extern async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
>  					    struct list_head *list);
> diff --git a/kernel/async.c b/kernel/async.c
> index 8663f5b..cb527b3 100644
> --- a/kernel/async.c
> +++ b/kernel/async.c
> @@ -65,6 +65,7 @@ static async_cookie_t next_cookie = 1;
> 
>  static LIST_HEAD(async_pending);
>  static LIST_HEAD(async_running);
> +static LIST_HEAD(async_running_no_sync);
>  static DEFINE_SPINLOCK(async_lock);
> 
>  static int async_enabled = 0;
> @@ -222,6 +223,28 @@ static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data,
>  	return newcookie;
>  }
> 
> + /**
> + * async_run_inatomic - in atomic contexts schedule a function for
> + * 			asynchronous execution

I'm not 100% sure whether kerneldoc likes split lines for the
description.

"async_run_inatomic - schedule a function for asynchronous execution from atomic context without checkpointing"
- but that's really a bit long...

> + *
> + * @ptr: function to execute asynchronously
> + * @data: data pointer to pass to the function
> + *
> + * Return zero if success, or else return others if failured

Returns zero on success, !zero on failure

> + * Note:

I'd move the description of the function's purpose before Note:.

> + * The purpose of this function is to offer a simple way to schedule an
> + * asynchronous thread from an atomic context, because there are not any
> + * functions which can create and start a kernel thread in atomic contexts
> + * now. 

I don't think the second part of the sentence is needed, this should
only be mentioned in the patch description. I'd rather add

"Since it does not return a cookie for checkpointing, it is for callers
that don't need later synchronization."

> We use async_running_no_sync as running list to make callers that
> + * don't want to synchronize on cookies, so can avoid some side effects for
> + * async_synchronize_full().

"async_run_inatomic() uses a distinct running list in order to avoid
slowing down synchronization within the general domain."

(The cookie will still be checked when __lowest_in_progress() returns
the cookie for the async_pending list, but I think that is negligible -
and it would be a general issue for special domains.)

> + */
> +int async_run_inatomic(async_func_ptr *ptr, void *data)
> +{
> +	return !__async_schedule(ptr, data, &async_running_no_sync, 1);
> +}
> +EXPORT_SYMBOL_GPL(async_run_inatomic);
> +
>  /**
>   * async_schedule - schedule a function for asynchronous execution
>   * @ptr: function to execute asynchronously

Btw: Do you have any specific use cases for this function in mind?
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